Bolaget gasaccumulator



TM. a. slb'smb'M. CRYSTAL DETECTOR FOR WIRELESS TELEGRAPHY.

APPLICATION FILED AUG. I7. 191-6.

1,319,804. "Patented Qct. 28,1919,

In verfi'or V Z I n v ,f A1

iron STATES n'runr OFFICE.

MARTIN GEORG SJ'fiSTRGM, OF UPSALA, SWEDEN, ASSIGNOB TO SVENSKA AKTIE-IBOLAGET GASACCUMULATOR, OF STOCKI-IOLM, SWEDEN.

CRYSTAL DETECTOR FOR WIRELESS TELEGRAPHY.

1,319.,Stl i.

Specification of Letters Patent.

Patented Oct. 28, 1919.

Application filed August 17, 1916. Serial No. 115,501.

To all whom it may concern:

Be it known that I, h Lin'riiv Gnonc SJosmen, subject of the King ofSweden, residing at Upsala, Sweden, have invented. new and usefulImprovements in Crystal Detectors for Wireless Telcgraphy, of which thefollowing is a specification.

in wireless telegraphy detectors are employed, which have for an objectto malze the currents of high frequency in the 0501i lating circuits ofthe receiving station perceptible. During the technical development ofsuch detectors efiorts have been made to construct a detector, whichpossesses a very high and simultaneously a very unchangeablesensibility. These eflorts have led to the construction of the so calledcrystal detectors, in which a conducting'pointed bar is pressed againstthe surface of a crystal piece. having a unipolar conducting power. Suchdetectors are very sensitive, they have however the incon enience, thata. very smalldisplacement of the point of contact between the pointedbar and the crystal piece results in considerable changes ofsensitiveness.

The inventor has found out the reason of this inconvenience of the saiddetectors and has found that in. the surface of the crystal some spotshave a positive action of transmitting the current in one direction onlyWhereas other adjacent spots have a negative action of transmission,that is to say, the current is in the second case transmitted in anopposite direction to the direction of transmissionin the first namedcase. Between the small spots within. which said action of the one orothcrlrind is very distinctly perceptible, other spots are present,within. which such action is very feeble or is not at all perceptible.Such spots are called neutral. if new the whole surface or part of thesurface of the crystal piece is brought in contact with a metallicconductor. and an alternating current is led through the surface ofcontact, the current will not be converted into a continuous current, asthe current in the one direction passes the positive and neutral spots,and in the other direction will 'be distributed over the negative andneutral spots. It will thus be necessa y for the purpose of ob-- taininga distinct transmission in. one di rection only to limit the contact toa spot;

having a powerful action of transmitting the current in one directiononly.

According to the present invention the surfaces of contact are made verysmall and the contact is adjusted in such a manner, that it embraces themost sensitive spot or spots. A contact of this kind is calledefiective, whereas the contact above described, having a large area, iscalled neutral.

For further illustration of the invention reference is made to theaccompanying drawing, in which Figure 1 is a side view of a detector ofthe type already known, whereas Fig. 2 is a side view partly in sectionof a detector according to the invention.

'Fig. 3 shows in side view partly in section a modified construction.

In Fig. 1 1 indicates a piece of a crystal and 2 a screw, the point ofwhich is pressed against the crystal piece. The screw 2 is carried by astandard3 of metal, fixed on an insulating base 1, carrying a metalplate 5, to which the crystal piece 1 is soldered. Conducting wires 6, 7are fixed in pole screws 8, 9 on the metal plate 5 and the standard 3respectively. The effective contact above referred to is established inthe construction according to Fig. 1 by pressing the point of the screw2 against the surface of the crystal piece 1, whereas the neutralcontact is obtained between the crystal piece 1 and the metal plate 5 orbetween said metal plate and the soldering metal of the crystal piece.In view of the fact that the sensitive spots of the surface of thecrystal piece have a very small area, it will be seen, that a slightdisplacement of the standard 3 or of the screw 2, such as will occur bya thrust, will decrease the sensitiveness of the detector veryCOI1Sl(lQ1ZLl')l)'. The sensitiveness is also dependent upon thepressure between the point of the screw and the crystal piece saidsensitiveness being greatest in case of a small pressure, and decreasingrapidly when the pi ssure is augn'iented. A variation of thetemperature, resulting in an irregular expansion of the parts of thedetector, is sufiic-ieut to establish variations of sensitiveness.making the detector incompetent as a means of measuring the intensity ofradiotelegraphic signals in a reliable manner.

According to the present invention in order to obviate theinconveniences of the efiective contact, previously employed in form ofa pressure contact, such a screw, a'metal spring or the like, a concreteor cohesive contact is used, the area of which is limited so as to coveronly a sensitive'spot of the surface of the crystal. Such a contact maybe established by soldering a very small metal ball or the like on thesaid spot.

According to the construction shown in Fig. 2 two metal plates 12, 13,provided with pole screws 14:, 15 for the conducting wires 16, 17 arefixed on an insulating base 10. On the plate 12 a crystal piece 18 issoldered. On the upper side of said crystal piece a very small metalball or the like 19 is so]- dered on a very sensitive place or spot,said ball 19 being electrically connected with the plate 13 by means ofa thin metal wire 20. The metal ball 19 may be fixed directly on thesensitive spot of the crystal piece, or said spot may be provided withan electrolytic cover ora metal powder cover, constituting the concreteor cohesive contact.

In order to protect and secure the contact it may be covered by aninsulating material,

4 such as a varnish.

Such concrete or cohesive contacts may be applied on several sensitivespots of the crystal surface, permitting the resistance and thescnsitiveness of the detector being varied within wide limits.

According to the construction shown in Fig. I) the neutral contact ismade concrete or cohesive. A crystal piece 21 is fixed in an insulatingcarrier 22, on which two metal plates 23, 24 are fixed, each of which iscon nected by a thin metal wire 25, 26 with a very small ball, solderedon the crystal pie e.

Having now described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A detector for wireless telegraphy comprising a crystal and a contactcohesively connected to only a sensitive spot on the crystal.

2. A detector for wireless telegraphy comprising a contact immovablysecured to the active material of the detector at a pre determined pointthereon.

In testimony whereof I have signed m name to this specification in thepresence of two subscribing witnesses.

MARTIN onono sJosrRoM.

Witnesses:

.WALDEMAR BoMAN,

Gama PRIEN.

